Timeline: on a trip this summer the Jake Brake switch's knob sheared off. I replaced it with an old one from the dash that wasn’t being used. It worked for most of our Black Hills trip, but then quit. I assumed the old switch was faulty and replaced it just before we left on this trip. I found out in the hills of Arkansas last week that the Jakes are still no joy. Today I dug deeper and checked a few more things before it got dark…

Checking voltage across the micro switch, it goes from 13.7 to about 3v when contacts are closed! Removing the micro switch from the equation and touching the lead to supply voltage produces no noise… I would think that the solenoids should click or something. I fire up the DD, go to fast idle, and then touch the wires to voltage and it doesn’t make any change in engine pitch or produce smoke.

I downloaded the Jacobs troubleshooting manual, but it mentions a lot of equipment I don’t have: DDEC, clutch switch, buffer switch, etc. All I have is the micro switch and the wire going into each bank.

Time to pop the valve covers??? Should I test each bank for voltage drop? Resistance??

Brian, when I had similar problems I started with applying DC power directly to each of the two leads going into the valve cover for the Jake brakes. With the engine off, I could hear a definite click when I applied or removed the power.

With that test completed I then started backtracking until I came to the circuit that was not operating. It ended up being the micro switch (buffer switch) on the throttle assembly. You should hear the click without much problem, as I recall.Richard

« Last Edit: November 06, 2006, 06:52:09 PM by DrivingMissLazy »

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Life should NOT be a journey to the grave with the intention of arriving safely in an attractive and well preserved body. But rather to skid in sideways, chocolate in one hand, a good Reisling in the other, body thoroughly used up, totally worn out and screaming: WOO HOO, what a ride

speakingof jakes, how do youknow if they are working? I mean my bus has them, and I had them checked "supposedly" when I first got it but there is still no difference when the switch is on. I don't hear them like I do when I hear a truck with them on. Am I supposed to hear them or just feel them slow the bus down?

It feels no different using the foot brake with the jake switch on or off so it stays off!

Ace, from my somewhat limited experience with them, a bus muffler generally does a good job of absorbing the sound of the Jakes. I had to turn my backup cam's volume up to actually hear them from the front seat. A Jake on a 4-stroke is much more efficient, and possibly louder by nature. And trucks sometimes route theirs to straight pipes.

You should, however, feel a distinct slowing and/or "holding back" anytime the tranny is in lockup and Jakes are engaged, even on flat ground. Mine will hold my bus at about a 5% grade and 1500-2000rpm in whatever gear I want to be in (2nd or 3rd lockup in my case). Steeper grades sometimes need some occassional help with a service brake nudge. Lesser grades need either throttle (which turns them off) or manual cycling of the switch. If I drove a lot of small grades I would want to add a bank selector to only energize one bank to "automate" the driving down.

Sounds like you might need to do some troubleshooting of yours, as well.

Ace, I would say that your Jakes are not working! Even with a good muffler I could still hear the difference in the exhaust. Especially if a window was open. Also, you should feel a definite braking action, and the higher the engine rpm the more braking action you feel. Even at slow speed in the 25-30 mph area you should feel braking action until the engine rpm drops to 1,000 rpm. If you can, take a ride with someone that has working Jakes. That is the easiest way to get that feel.Richard

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Life should NOT be a journey to the grave with the intention of arriving safely in an attractive and well preserved body. But rather to skid in sideways, chocolate in one hand, a good Reisling in the other, body thoroughly used up, totally worn out and screaming: WOO HOO, what a ride

Brian, you can try applying voltage to the wires on the heads while the engine is running, but you need to rev the engine up to get the oil pressure up high enough to work the jake heads, 20-30 psi. If the jakes start coming on then it is an electrical problem. With the micro switch closed you should have full voltage across the switch.Lloyd

You do not need to start the engine to determine if it is an electrical problem. I would do the check that Lloyd recomends after you first determine that the solenoids inside the valve cover are working. This audible check also determines that both sides are working. By doing this I found out that only one side of mine were operating. Had to pull the valve cover to fix that.Richard

Brian, you can try applying voltage to the wires on the heads while the engine is running, but you need to rev the engine up to get the oil pressure up high enough to work the jake heads, 20-30 psi. If the jakes start coming on then it is an electrical problem. With the micro switch closed you should have full voltage across the switch.Lloyd

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Life should NOT be a journey to the grave with the intention of arriving safely in an attractive and well preserved body. But rather to skid in sideways, chocolate in one hand, a good Reisling in the other, body thoroughly used up, totally worn out and screaming: WOO HOO, what a ride

I tore into the heads this morning. It turns out the pax side solenoid on the forwardmost head (mine's a V-drive) is robbing voltage from the switch. As Murphy would have it, it was the hardest one to reach. I had to take off the air inlet "horn" and wedge myself under the cap to get to it. I also promptly lost a tiny 6-32 elec. screw down inside the head and it took an hour of probing... and a pencil magnet that also got stuck down in the head whilst trying to retrieve it. When it rains it pours! So... ten minutes to troubleshoot, and over an hour to "pick up the pieces".

Anyways, the solenoid is probably either defective itself, or the linkage is messed up somehow. Strangely, it dosen't look like the other three. It has a black metal head (the others are bare metal) and a different wire assembly. I took it off of the Jake assembly so I can bench test it. Hopefully, I can find a replacement around the Dallas, TX area... maybe a Stewart & Stevenson or similar. If not, I guess 75% of the cylinders are better than none. No real grades between here and home, anyways. But I do have time to work on it while here.

Well Brian I think you have came up with a new term in the electrical industry. LOL. I never heard of this "forwardmost head (mine's a V-drive) is robbing voltage from the switch." What do you mean exactly? Did the other solenoids actuate when you dis-connected this one? If so, you could just leave that one disconnected until you get home. Richard

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Life should NOT be a journey to the grave with the intention of arriving safely in an attractive and well preserved body. But rather to skid in sideways, chocolate in one hand, a good Reisling in the other, body thoroughly used up, totally worn out and screaming: WOO HOO, what a ride

It was just my layman's way of saying, there's no voltage drop with either of the other three (or all three) when voltage is applied to them... and the others all click, the way they're supposed to. Trying to actuate the offending one drops voltage to near 3v and it doesn't click. I'm assumiing there's a bad coil in it. When it's attached to the others, none of 'em work. "Robbing" voltage, eh?

I don't mind doing the work while I'm here. The head's already opened up anyway. And I'm probably more likely to find the part here than I am in Denver. Besides, I'm sorta waiting around for the weekend, anyway. When at home, "honey-do" trumps bus duties 99.9% of the time!

Any truck dealership should have a solenoid for you good job there guy.

LarryH

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Great Brian. Thanks for the explaination. I agree that you have definitely proved that you have one bad solenoid that is shorted to ground and dropping the input voltage so that the other solenoids can not operate. Probably would have had a circuit breaker tripping before long.

Anyhow, excellent troubleshooting and I am glad you found the problem. Richard

It was just my layman's way of saying, there's no voltage drop with either of the other three (or all three) when voltage is applied to them... and the others all click, the way they're supposed to. Trying to actuate the offending one drops voltage to near 3v and it doesn't click. I'm assumiing there's a bad coil in it. When it's attached to the others, none of 'em work. "Robbing" voltage, eh?

I don't mind doing the work while I'm here. The head's already opened up anyway. And I'm probably more likely to find the part here than I am in Denver. Besides, I'm sorta waiting around for the weekend, anyway. When at home, "honey-do" trumps bus duties 99.9% of the time!

Thanks!Brian

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Life should NOT be a journey to the grave with the intention of arriving safely in an attractive and well preserved body. But rather to skid in sideways, chocolate in one hand, a good Reisling in the other, body thoroughly used up, totally worn out and screaming: WOO HOO, what a ride

I was able to find a new solenoid at Stewart & Stevenson, only ten minutes from my folks' home. Out the door for barely less than a C Note. The replacement part matched the other three, so I'm really suspecting that the defective one failed because the installer used the wrong part or a used one. The Jakes were put on less than 10k miles ago, so I have a hard time believing a new/correct part would fail so quick.

I screwed in the part, connected the harness and re-tested the switch... only about 1 volt dropped now, and a definite CLICK. I replaced the microswitch and cleaned up all the connections, since I was "in the area" anyways. Fired up the DD, went to high idle, and flipped on the Jakes... "bbbbllllattt cough cough." I heard the distinctive tone louder than I ever had... probably because it was being fueled, but maybe it's because my Jakes had always been hampered by the "wrong" solenoid. Only way to know for sure is a test drive. Tomorrow, perhaps.

Below is a shot of the two parts... old and replacement. The silver one matches the other three. It also has a much smaller hole in the end.

Life should NOT be a journey to the grave with the intention of arriving safely in an attractive and well preserved body. But rather to skid in sideways, chocolate in one hand, a good Reisling in the other, body thoroughly used up, totally worn out and screaming: WOO HOO, what a ride